FIELD OF THE INVENTION
This invention pertains to a fixed bed reactor or absorption tower having liquid and gas bypasses, and more particularly to such apparatuses having a low pressure drop during the bypassing of liquid and gas across the fixed bed.
In the normal operation of fixed bed hydroprocessing oil refining reactors, the top of the catalyst bed often becomes fouled or plugged by the deposition of organometallic compounds, polymeric and carbonaceous materials and particulates. The plugging of the catalyst bed is undesirable, since the resultant increase in pressure drop necessitates costly shut-downs and requires time-consuming repairs and maintenance.
In an effort to overcome this problem many schemes have been devised, wherein each reactor is provided with more than one catalyst bed, and a plugged bed is bypassed to extend the operating life of the reactor.
One such bypass scheme is shown in U.S. Pat. No. 3,509,043, issued: Apr. 28, 1970. In this reactor, catalyst bed bypass tubes are used which contain rupture discs. These rupture discs are designed to burst open when the initial catalyst bed becomes fouled, and when a predetermined pressure drop is reached within the reactor. Under normal circumstances this bypass design will provide a workable means for extending the operability of the reactor. However, such a system is particularly sensitive to upsets in the feed flow rate of the reaction materials. These upsets can often cause a premature bursting of the rupture discs.
Another U.S. patent illustrating the use of rupture discs is illustrated in U.S. Pat. No. 3,796,655 issued: Mar. 12, 1974.
In this system, the bypassed material is directed upwardly in order to provide a dislodging backflow, and thus, unfoul the crusted or plugged catalyst bed.
The bypassing schemes of these and other inventions achieve bypassing of the fouled catalyst bed with low pressure drop. High pressure drop bypassing is undesirable since the higher pressure drop necessitates the use of larger and more expensive pumps and compressors in order to maintain the flow rate of the materials through the reactors. The low pressure drop for bypassing is achieved by employing a moving or a destructible component such as a rupture disc. These moving or destructible components are not reliable and may fail to operate or may operate prematurely.
The subject invention provides an improved bypass apparatus, wherein a low pressure drop bypass is achieved without the use of a moving or a destructible component, and further wherein the on-time of the reactor is extended several fold.